With development of mobile Internet technologies, a communications system such as a Long Term Evolution (LTE) system can provide a 100 megahertz (MHz) or even higher bandwidth.
In addition, communication services are increasingly diverse. For example, from a service type perspective, there is a conventional service such as a voice service or a short message service and also a big data service such as a video service or a high-definition image service. From a transmission rate perspective, there is a low-rate service and also a high-rate service. Different services have different requirements for a bandwidth of a frequency domain resource. For example, if a user has a relatively low bandwidth requirement, to reduce costs, there may be a terminal device with relatively low processing performance (for example, the terminal device can process transmission only on a frequency domain resource with a relatively low bandwidth). Consequently, the terminal device with relatively low performance cannot be used in the foregoing high-bandwidth system.
How to flexibly meet different user requirements in a high-bandwidth communications system becomes an urgent problem to be resolved in the industry.